Current standards for managing group communications are for example the TETRA or TETRAPOL standards. They operate according to a broadcast distribution mode. With the new communication standards, for example the MCPTT standard, general public communication networks, which have a national coverage, are however susceptible of being involved. These communication networks mainly have a unicast distribution mode, that is to say point to point.
Furthermore, the technical specifications 3GPP—24.379 (clauses 13 and 14) and 24.380 (clauses 6.4 and 10) describe the management of communications consisting in exchanges between client terminals and participation functions, hosted on at least one server type electronic device. These specifications take into account the broadcast distribution mode of the MBMS service of LTE but only manage the case where the set of participation functions are situated in a same geographic zone, and where it is not necessary to have exchanges between these different participation functions to manage the distribution to the client terminals in an optimal manner.
However, new group communication standards aim henceforth to use communication systems that involve a broadcast distribution participation function (also designated as “broadcast distribution participation function”, or as “broadcast participation function”), and a unicast distribution participation function (also designated as “unicast distribution participation function”, or as “unicast participation function”) covering a potentially large number of client terminals and distributed over an extended territory.
Consequently, in practice, the broadcast participation function, on account of the extended territory that it has to cover, is distributed over different broadcast distribution entities, and the unicast participation functions, on account of the large number of terminals that the communication system has to manage, is also distributed between different unicast distribution entities, these distribution entities corresponding to communication modules integrated in servers, or to servers themselves.
The mobility of the client terminals, also designated as “clients”, as well as the possibility that these terminals have to become affiliated, or no longer be affiliated, to a given communication group, leads to situations where the optimisation of distribution resources to the terminals is beneficial.
Thus, for example, if a given communication group that is distributed over an extended territory is considered, communications with the terminals of this group will be conducted necessarily in unicast mode.
Yet, for example in the case of a group of firefighters gathering together for a given response at a same place, the unicast distribution mode initially adopted is no longer optimal in terms of economy of radio resources when the different terminals are located near to each other: a large part of the terminals of this group henceforth being situated in a same zone, it is judicious to switch over to a broadcast distribution mode for these terminals.
Nothing in the current standards provides, for such group communications, for such a switch over in the case where the system comprises a multiplicity of unicast distribution entities and a multiplicity of broadcast distribution entities on account of the number of client terminals managed and of the geographic extent covered.